From owner-freebsd-mobile Sat Aug 17 13:16:27 2002 Delivered-To: freebsd-mobile@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id BEB0937B400 for ; Sat, 17 Aug 2002 13:16:24 -0700 (PDT) Received: from harmony.village.org (rover.bsdimp.com [204.144.255.66]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9FA5B43E4A for ; Sat, 17 Aug 2002 13:16:23 -0700 (PDT) (envelope-from imp@bsdimp.com) Received: from localhost (warner@rover2.village.org [10.0.0.1]) by harmony.village.org (8.12.3/8.12.3) with ESMTP id g7HKGKQe010640; Sat, 17 Aug 2002 14:16:21 -0600 (MDT) (envelope-from imp@bsdimp.com) Date: Sat, 17 Aug 2002 14:15:37 -0600 (MDT) Message-Id: <20020817.141537.108956335.imp@bsdimp.com> To: fscked@pacbell.net Cc: eyurtese@turkuamk.fi, mobile@FreeBSD.ORG Subject: Re: IBSS and BSS with multiple FreeBSD Wireless Gateways From: "M. Warner Losh" In-Reply-To: <3D5E98FF.82CD061E@pacbell.net> References: <3D5E98FF.82CD061E@pacbell.net> X-Mailer: Mew version 2.1 on Emacs 21.2 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-mobile@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org In message: <3D5E98FF.82CD061E@pacbell.net> richard childers writes: : You are WiFi- and FreeBSD-enabled; so is your friend. For the sake of : simplicity let's assume that you are directly across from one another in two : dormitories at approximately the same height. : : You both eliminate signal strength and signal security issues with : line-of-sight antenna pointed directly into one another's cone of : transmission. Well, except that it is real easy to intercept the side lobes of most antennas if you have proximity. I routinely am able to sniff packets off of dish antennas that have a very small cone of transmission by being very close. : At this point you are not unlike two routers with a cable between them, and : it is only a matter of picking an appropriate class 'C' subnet (IE, : 192.something), assigning it an appropriately long mask (IE, one preserving : only two bits of the address for actual networking), bringing the interfaces : up and adding routing entries on each end. Yes. I'm doing exactly what you suggest over 5.5 miles between my house and a friend's. : Note that your network is still hypothetically subject to eavesdropping and : jamming from parties in either antenna's line of sight. This is a real threat. : A slightly more complicated scenario emerges when you attempt to add a third : node; at this point one of the nodes needs to have two cards, with two : addresses and two antennas and two routing entries. : : I imagine there are some issues with crosstalk between the antennas that : would need to be addressed with physical separation and maybe some : appropriate shielding; tin foil works, I expect. Tinfoil won't cut it, I'm afraid. I've tried to shield things with tinfoil and found that it was woefully inadequate, even when well grounded. Cross talk between antennas is a real problem. I have two on my roof and have found that if I run them at the same frequency that there are big problems. I have to run them at different frequencies to make that work. And I gotta make sure that any access points I have inside are on a third frequency, otherwise you get mutual interference when there's lots of traffic. Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-mobile" in the body of the message